Enzyme-assisted extraction of polyphenol from edible lotus (Nelumbo nucifera) rhizome knot: Ultra-filtration performance and HPLC-MS2 profile.

Rhizome knot is always wasted as useless and inedible part of lotus root, despite its abundance of polyphenols. In this work, enzyme-assisted extraction followed by ultra-filtration was investigated to recover polyphenols from rhizome knot. Cellulase and pectinase treatment enhanced the polyphenols extraction. The 100 kDa membrane resulted in better filtration yield than 50 kDa membrane, 3.84% and 3.37%, respectively. With 100 kDa membrane, the highest filtration yield (4.08%) was achieved with a rotational speed of 600 rpm, TMP of 0.3 MPa and pH of 5. Satisfied permeate turbidity (<3 NTU) and polyphenol transmission (>90%) were obtained under these conditions. The main polyphenols identified in both rhizome knot extract and permeate were: chlorogenic acid, B-type procyanidin dimer·H2O, (+)-Catechin, B-type procyanidin dimer, (-)-Epicatechin, propyl gallate·H2O, caffeic acid, (-)-Epicatechin-3-gallate, and rutin. Membrane fouling led to the most important resistance (58% of total resistance). Scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) evidenced that protein accumulation was the main fouling cause.